The present invention relates to a fire resistant cable. More particularly, the present invention relates to a fire resistant electrical or data cable which is capable of continuing to operate and maintain circuit integrity for a certain period of time when subjected to fire. The cable of the present invention is also resistant to water and mechanical stresses, such as those caused by the water jets used in fire-extinguishing operations.
As known, for example, from CEI EN 50200 and CEI 20-22/2, an electrical or data cable resistant to fire (known as a “fire resistant” cable) is a cable configured so as to be capable of continuing to function with acceptable performance even if, owing to a fire, it is exposed to a direct flame for a period of time, at temperatures of up to 800° C.-900° C. or above.
Fire resistant cables are used for various purposes in the fields of civil constructions and transportation, where they are used, for example, in emergency lightings, alarm and automatic fire detection systems, fire extinguishing systems, automatic emergency exits, lift systems, activation of smoke outlets or shutters, fans, air conditioning, and telephone and video surveillance systems.
In the state of the art, fire resistant cables are known which comprise compositions forming a fire resistant ceramic at elevated temperatures. US 2006068201, for instance, describes electrical cables comprising an insulating layer and/or a sheathing for providing a fire resistant ceramic under fire conditions, the insulating layer and/or sheathing layer comprising:                at least 15% by weight based on the total weight of the composition of a polymer base composition comprising at least 50% by weight of an organic polymer;        at least 15% by weight based on the total weight of the composition of a silicate mineral filler, and        at least one source of fluxing oxide which is optionally present in said silicate mineral filler, wherein after exposure to an elevated temperature experienced under fire conditions, a fluxing oxide is present in an amount of from 1 to 15% by weight of the residue.        
The fluxing oxide is likely to be boron oxide or a metal oxide selected from the oxides of potassium and sodium. A precursor of the fluxing oxide can be a metal carbonate precursor to the metal oxides. Zinc borate is a useful precursor for boric oxide. The composition may contain silicon dioxide as a result of being exposed to elevated temperature. Silica may also be added as a separate filler component.
WO 2010/142917 discloses an electrical cable that includes an insulation layer including a first polymer layer surrounding the electric conductor, the first layer being obtained from a first composition including a matrix polymer formed from a thermoplastic polymer, and at least one ceramic-forming charge. The insulation layer further includes a second cross-linked polymer layer surrounding said first layer, the second layer being obtained from a second composition including a matrix polymer containing polyolefins and substantially free from any ceramic-forming charge or halogen compound.
The ceramic-forming charge can be selected from a meltable ceramic charge and a refractory charge or mixture thereof. The meltable ceramic charge can be at least one mineral charge selected from zinc borate. The refractory charge can be at least one mineral charge selected from magnesium oxide, calcium oxide, aluminium oxide, silicon oxide. The second composition can comprise a mineral charge different from that of the first composition, for example magnesium hydroxide or aluminium trioxide. The mineral charge can also be a carbonate. The second composition comprises at least 90 parts by weight of mineral charge for 100 parts by weight of polymer.
WO 2011/112704 relates to insulation and cable jackets with micro oxide particles used with cable and cable components for increasing the flame retardancy. In particular, the insulation material and/or the jacket and/or the bedding include micro oxide particles to form a composite. Preferred oxides include silicon, aluminium, magnesium and their double oxides. Zn and Fe oxides may also be suitable for some embodiments. The micro oxide particles are preferably solid non porous amorphous particles. The micro oxide particles may be added to polyethylene or ethylene vinyl acetate. The concentration of the micro oxide particles may be about 1 to 80% by weight of the insulation, and most preferred about 3-25%. The composite insulation may include alumina trihydrate, magnesium hydroxide, zinc borate.